Heretofore, a well known throttle valve apparatus has a throttle valve, a full open stopper and a full close stopper. The throttle valve controls the amount of air taken into an engine. The full open stopper restricts rotation of the throttle valve in its first rotational direction when the throttle valve is fully opened. The full close stopper restricts the rotation of the throttle valve in its second rotational direction, which is opposite to the first rotational direction, when the throttle valve is fully closed. One of the throttle valve apparatus is disclosed in JP-A-H11-132061.
In the throttle valve apparatus, the full open stopper and the full close stopper respectively project from different positions of an outer surface of a bore portion of a throttle housing. The full open stopper receives excessive load when the throttle valve is fully opened. Moreover, the full close stopper receives the excessive load when the throttle valve is fully closed. Accordingly, each of the full open stopper and the full close stopper is required to be formed in a shape to be able to endure the load. Therefore, the full open stopper and the full close stopper are formed to be enlarged, so that the material cost is disadvantageously increased.
Moreover, when the bore portion, the full open stopper and the full close stopper are integrally formed by means of resin molding or metal casting, and unless wall thicknesses of which are formed uniformly, a delicate point, a void or a blow hole is likely to be formed therein. Accordingly, the full open stopper and the full close stopper disadvantageously reduce their performance and durability.